In a large saucepan, melt the chocolate and butter, stirring frequently, until evenly melted. Set aside to cool down to warm, about 10 minutes. Stir in the sugar and then, one at a time, the eggs. Stir in the vanilla extract and the espresso powder.

In a medium bowl, stir together the flours, cocoa powder, baking powder, and salt. Stir the dry ingredients into the wet ingredients. The batter will have the sticky consistency of brownie batter.

Scrape the batter onto a sheet of plastic wrap and wrap the dough into a large ball. Place in the fridge for at least two hours (up to eight hours) or in the freezer for 30 minutes, to firm up the dough.

When ready to bake, preheat the oven to 350 degrees. Place parchment paper or silicone baking mats on cookie sheets.

Put the powdered sugar into a small bowl. Roll chunks of the chilled cookie dough into 1-inch balls, then roll the balls in the powdered sugar until evenly coated. Arrange the balls about 1½ inches apart on the cookie sheets.

Bake for 8 to 12 minutes (the baking time will vary, depending on how cold the cookie dough is), until puffed and cracked on top. Remove from the oven and let cool for a few minutes before removing the cookies with a spatula to wire racks to finish cooling.

Serve warm or at room temperature. Keep in an airtight container for a few days. (Do not freeze, as freezing makes the powdered-sugar coating soggy.)

Note

You can use all ordinary flour for this recipe, if you don't have whole-wheat pastry flour on hand.